1. Field of the Invention
An aspect of the present invention relates to a pixel and an organic light emitting display device using the same, and more particularly, to a pixel and an organic light emitting display device using the same, which can improve image quality.
2. Description of the Related Art
Recently, various types of flat panel display devices capable of reducing the weight and volume of cathode ray tubes have been developed. The flat panel display devices include a liquid crystal display, a field emission display, a plasma display panel, an organic light emitting display device, and the like.
Among these flat panel display devices, the organic light emitting display device displays images using organic light emitting diodes that emit light through recombination of electrons and holes. The organic light emitting display device has a fast response speed and is driven with low power consumption.
An organic light emitting display device has a plurality of pixels arranged in a matrix form at intersection portions of a plurality of data lines, a plurality of scan lines and a plurality of power lines. Each of the pixels generally includes an organic light emitting diode, two or more transistors including a driving transistor, and one or more capacitors.
The organic light emitting display device has low power consumption. However, in the organic light emitting display device, the amount of current that flows in an organic light emitting diode is changed depending on the variation in the threshold voltage of the driving transistor included in each pixel, and therefore, images with unequal luminance are displayed. That is, characteristics of the driving transistor are changed depending on the fabrication factor of the driving transistor included in each pixel. Practically, it is impossible in the current fabrication process to fabricate the organic light emitting display device so that all transistors of the organic light emitting display device have the same characteristics. Accordingly, the variation in the threshold voltage of the driving transistor occurs.
To solve such a problem, a method of adding a compensation circuit including a plurality of transistors and capacitors to each pixel has been proposed. The compensation circuit compensates for a variation in threshold voltage of a driving transistor by allowing the driving transistor to be diode-coupled during a period of supplying a scan signal. Here, a gate electrode of the diode-coupled driving transistor is initialized to a negative initialization power source and then receives a data signal supplied.
However, in a case where the gate electrode of the driving transistor is initialized using the initialization power source in the conventional method, an image with a desired luminance is not displayed by leakage current. In other words, a leakage path is formed from the gate electrode of the driving transistor to the initialization power source, and an image with a desired luminance is not displayed by leakage current through the leakage path.
Conventionally, a structure in which two capacitors is included in a compensation circuit was proposed. However, in a case where the two capacitors are included in the compensation circuit, an undesired image, e.g., a blurred image is displayed by a change in capacitance between the capacitors due to process tolerance. In other words, in a case where the two capacitors are included in the compensation circuit, a predetermined ratio should be maintained between the capacitances of the two capacitors. If the capacitance of one of the two capacitors is increased, the predetermined ratio is not maintained, and accordingly, image quality is deteriorated.